MPLS TE Class-Based Tunnel Selection (CBTS) enables the SP to dynamically route and forward traffic of different classes of service (CoS) into different TE tunnels between the same tunnel headend and the same tailend where the tunnels can be DS-TE aware. The set of TE (or DS-TE) tunnels from same headend to same tailend that are configured to carry different CoS values is referred to as a "tunnel bundle." After configuration, CBTS dynamically routes and forwards packets into the tunnel that is configured to carry the CoS of the packets.

Figure 14-39 shows the base configurations for all devices in the network prior to the implementation of CBTS. The base configurations show the implementation of three static (explicit) tunnels on the PE1-AS1 router.

Figure 14-40 outlines the configuration flowchart for the implementation of CBTS, as well as the configuration of the PE1-AS1 router to implement CBTS.

Figure 14-40. Case Study 6: Configuration of CBTS

As shown in the highlighted section in Figure 14-40, the configuration of the PE1-AS1 router shows that Tunnel1 transports packets with MPLS EXP value of 5, Tunnel2 transports packets with MPLS EXP values of 3 and 4, and Tunnel3 is used to transport packets of all other MPLS EXP values.

CBTS supports tunnel selection based on the value of the EXP field that the headend router, taking into account the input Modular QoS CLI (MQC), imposes on the packet. If the input MQC modifies the EXP field value, MPLS TE CBTS uses the modified value for its tunnel selection. It is important to note that if the output MQC modifies the EXP field, CBTS ignores the change in the EXP value.

Verification of Class-Based Tunnel Selection

Verification of CBTS is shown in Figure 14-41. Verification of tunnel status by issuing a show MPLS traffic-eng tunnels brief on PE1-AS1 is shown along with verification of TE topology and next-hop pointing to all three tunnels and tunnel association into IGP.

Figure 14-41. Case Study 6: Verification of CBTS

Final Configurations for Case Study 6

The final configurations for Case Study 6 for the PE Routers PE1-AS1 and PE2-AS1 to implement CBTS are shown in Figure 14-42. For all other device configurations, refer Figure 14-39.